Multi tube heat exchanger

ABSTRACT

Heat exchanger for heat exchange or heat recovery in systems such as refrigeration or heat pump systems, in particular a condenser or evaporator in such systems The heat exchanger is shaped of a multi-port aluminium extrusion ( 8 ) by bending and forming parallel loops. Each of the ends of the extrusion ( 8 ) are finally bent such that they are facing each other and are connected at an offset of one port or hole ( 9 ) and thereby creating a single helical loop unit with inlet and outlet ports ( 15  respectively  16 ).

The present invention relates to a heat exchanger for heat exchange or heat recovery in systems such as refrigeration or heat pump systems, in particular a condenser or evaporator in such systems.

Many soft drink dispensers and display coolers use a steel heat exchanger as the condenser unit in their refrigeration system. The steel heat exchanger is commonly manufactured as a two piece construction made of steel tubing and steel sheet material or wire which are bonded to each other by mechanical fastening means or tack welding and then finally shaped to the desired shape (se later description). A heat exchanger of the tube and sheet type is for instance known from U.S. Pat. No. 7,140,25.

However, the thermal capacity of the steel heat exchanger or condenser is limited by two major factors namely the thermal conductivity and the physical connection (usually tack weld) between the tube and the sheet/wire which reduces the energy transfer and represent a bottleneck for the thermal flow. Besides, even though the steel material as such is cheap compared to other metals used in heat exchangers, the manufacturing is relatively expensive due to the number of manufacturing steps.

From U.S. Pat. No. 4,852,233 and U.S. Pat. No. 5,729,995 are further known different types of extruded, flat multi port (multi hole) tube heat exchangers of aluminium where the tube is folded into parallel tube loops forming a rectangular heat exchanger “stack” with an inlet at one end and outlet at an other end for the fluid to be circulated. A disadvantage with these known extruded multi tube solutions is the use of end manifold to interconnect the ports at each end which represent an extra cost to manufacture and assemble. Besides, the heat transfer efficiency is reduced due to poor fluid circulation.

There are also known heat exchangers and condensers of other metals, in particular, copper, but these have not found any extensive use, partly because of high material and manufacturing costs.

With the present invention is provided a heat exchanger, in particular a condenser for refrigeration systems, which is simple and cheap to manufacture and which has high thermal efficiency.

The invention is characterized by the features as defined in the attached independent claim 1.

Preferred embodiments of the invention are further defined in the independent claims 2-5.

The invention will be further described in detail in the following by means of examples and with reference to the attached drawings, where:

FIG. 1 shows in perspective view part of a commonly known refrigeration system, including a compressor and steel condenser with connecting piping,

FIG. 2 shows a perspective view of a tube and sheet element of a conventional steel condenser prior to bending.

FIG. 3 shows the same element as in FIG. 2 after bending, and

FIG. 4 shows a perspective view of an extruded multi port (multi channel or hole) element from which the heat exchanger according to the invention is made,

FIG. 5 shows in much larger scale a cross section of the extruded element shown in FIG. 4,

FIG. 6 shows the extruded element bent to its final shape forming a heat exchanger according to the invention.

As stated above, FIG. 1 shows in perspective view part of a commonly known refrigeration system for a drink dispenser or display cooler unit. The figure does not show a complete refrigeration system, but just the compressor 1 and steel condenser 2, as well as some connecting piping for such system. The condenser shown in FIG. 1 is as stated a steel pipe type with wire mesh for improved heat transfer. Moreover, the steel heat exchanger is manufactured as a two piece construction made of steel tubing and steel wire mesh or sheet metal which is tack welded together.

FIGS. 2 and 3 shows an example of a known steel heat exchanger or condenser based on steel tubing and steel sheet element where the steel tube 3 is first bent into a serpentine so that the inlet 4 and outlet end 5 are on the same side and where a sheet metal 6 is tack welded together with the tube 3. After the two steel parts 3, 6 are joined the condenser element is spray painted for extra corrosion protection and the condenser is finally formed by bending the tack welded tubing and sheet into a serpentine or square as shown in FIG. 2.

The thermal capacity of the steel condenser is, however, as stated above limited by two major factors, namely the thermal conductivity of steel which is 43 w/m k, and the physical connection (tack weld) between the tube and the sheet/wire which represents a bottleneck for the thermal flow.

FIGS. 4-6 show the heat exchanger 10 (see in particular FIG. 6—finished product) according to the invention. More precisely FIG. 4 shows the multi-port aluminium extrusion 8 of which the heat exchanger according to the invention is made, and FIG. 5 shows in larger scale a cross section such extrusion. Its initial shape is a longitudinal extruded element or bar 8 formed as a flat “sheet” 11 with interconnected ports or holes/channels 9.

When producing the heat exchanger 10, the extrusion 8 as shown in FIGS. 4 and 5 is bent from the middle part and outwards in parallel loops like a serpentine and finally forming a rectangular heat exchanger “package” as shown in FIG. 6. The two ends of the extrusion are bent such that they are facing each other, as is further shown in the FIG. 6, and are connected at an offset of one port or hole 9. This is preferably done by means of small connecting tubes 12 inserted and brazed in between the ports or holes 9 facing each other from each end of extrusion element 8, and thereby creating a single helical loop unit with inlet and outlet ports, 15 respectively 16, preferably provided with pipe connectors 13, 14 braced thereto. The connecting tubes 12 and inlet/outlet connectors 13, 14 may be of any suitable material such as aluminium or copper.

Alternatively, instead of separate connectors 12, 13, 14, the ends of the extrusion may be mechanically processed to remove excess material between the ports 9 of the extrusion thereby using the ports 9 as such as connectors.

This heat exchanger according to the invention requires no “return bends” and it offers a rigid construction.

Thermal tests on the inventive aluminum condenser has revealed that it has a far better thermal capacity per square unit in comparison to the commonly used steel condensers that is dominating the market today, and the present invention may therefore substitute the condenser solutions made of steel.

The thermal conductivity of aluminum is 250 w/m×k which far superior to steel and the profile is extruded in one piece which offers the best possible heat transfer bridge between the media in side the tube and the air passing the exterior of the profile. The aluminium extrusion solution according to the invention further eliminates several manufacturing process steps such tube serpentine bending, tack welding to sheet/wire and painting.

Aluminum is by nature self protecting against corrosion due to its ability to create a self healing oxide layer. Should there be a need for further corrosion protection it is possible for instance to zink arc spray the profile or use a long life alloy such as 300048 or a combination of both.

The idea of using an extruded aluminum profile and then offsetting the ends according to the present invention further reduces the overall production process and thereby the production cost significantly.

The invention as defined in the claims is not delimited to the example as described above and shown in the figures. Thus, the heat exchanger can be used, not only as condenser in a refrigeration system, but in any system where heat is exchanged or recovered. 

1-5. (canceled)
 6. Heat exchanger for heat exchange or heat recovery in systems such as refrigeration or heat pump systems, in particular a condenser or evaporator in such systems, the heat exchanger being shaped of a multi-port aluminium extrusion by bending and forming parallel loops, wherein each of the ends of the extrusion are finally bent such that they are facing each other and are connected at an offset of one port or hole and thereby creating a single helical loop unit with inlet and outlet ports.
 7. Heat exchanger according to claim 6, wherein the ports are connected by means of small connecting tubes inserted and brazed in between the ports or holes facing each other from each end of the extrusion.
 8. Heat exchanger according to claim 6, wherein the inlet and outlet ports each are provided with pipe connectors which are braced thereto.
 9. Heat exchanger according to claim 6, wherein the ends of the extrusion is mechanically processed to remove excess material between the ports of the extrusion whereby the ports as such are used as connectors.
 10. Heat exchanger according to claim 6, wherein the connecting tubes and inlet/outlet connectors of a suitable material such as aluminium or copper.
 11. Heat exchanger according to claim 7, wherein the connecting tubes and inlet/outlet connectors of a suitable material such as aluminium or copper.
 12. Heat exchanger according to claim 8, wherein the connecting tubes and inlet/outlet connectors of a suitable material such as aluminium or copper. 